Neutrino
Definition
The ghost particle — nearly massless, chargeless, and so aloof that trillions pass through you every second unnoticed.
Symbol: ·
Technical definition
An elementary lepton with near-zero mass and no electric charge, interacting only via the weak force (and gravity). Three flavors (electron, muon, tau), produced in beta decay and stellar fusion. About 65 billion solar neutrinos pass through each square centimeter of Earth per second.
Example
The Sun's core emits neutrinos that reach Earth in 8 minutes — and zip straight through the entire planet as if it were not there.
Neutrinos are not ‘nothing’ — they have tiny but nonzero mass (proven by flavor oscillation) and carry real energy away from reactions. They were long thought massless, but oscillation experiments proved otherwise.